1. Field of the Invention
Aspects of the present invention relate to a benzoxazine-based monomer, a polymer thereof, an electrode for a fuel cell including the same, an electrolyte membrane for a fuel cell including the same, and a fuel cell using the same. For purposes of this application, “benzoxazine-based monomer” shall mean that the aromatic ring may contain up to 2 nitrogens within the ring. Single ring and fused ring substituents are attached to the pendent nitrogen. The ring substituents may be heterocyclic.
2. Description of the Related Art
Fuel cells using a polymer electrolyte membrane as an electrolyte, which operate at a relatively low temperature and can be miniaturized, are regarded as an alternative power source for automobiles and for residential distributed power generation systems. A known polymer electrolyte membrane used in polymer electrolyte membrane fuel cells are the perfluorosulfonic acid polymers represented by NAFION® (DuPont Company).
However, these polymer electrolyte membranes must be hydrated to retain proton conductivity. In addition, the fuel cell system needs to be operated at 100° C. or higher in order to improve the system efficiency. However, the electrolyte membrane cannot function as a solid electrolyte at such a high temperature since moisture evaporates from the electrolyte membrane.
A non-hydrated electrolyte membrane that can be operated at 100° C. or higher has been developed in order to overcome these problems. For example, polybenzimidazole doped with phosphoric acid as a material used to form a non-hydrated electrolyte membrane is disclosed in U.S. Pat. No. 5,525,436.
In addition, in fuel cells using a perfluorosulfonic acid polymer membrane that operates at a low-temperature, a hydrophobic electrode obtained by mixing the perfluorosulfonic acid polymer with water-repellent polytetrafluoroethylene (PTFE) is used in order to improve gas diffusion that is otherwise blocked by water generated in a cathode (Japanese Patent Laid-Open Publication No. hei 05-283082).
Meanwhile, in fuel cells using polybenzimidazole (PBI) doped with phosphoric acid, which is a high-temperature non-hydrated electrolyte for an electrolyte membrane, attempts to impregnate an electrode with liquid state phosphoric acid have been made and attempts to increase the loading amount of a metal catalyst have been made in order to facilitate interface contact between the electrode and the membrane. These attempts, however, do not sufficiently improve characteristics of the fuel cells.
When air is supplied to a cathode in a solid polymer electrolyte membrane doped with phosphoric acid, activation takes about a week even if the electrode composition is optimized. Although a fuel cell can have improved efficiency and activation time can be decreased by replacing air with oxygen, the use of oxygen is not preferred for commercialization.